Lane Detection

Detect road lanes for autonomous driving applications.

View Source Code

Overview

Detect lane markings on roads using classical computer vision techniques. Foundation for self-driving car systems.

Key Techniques:

  • Canny edge detection
  • Region of interest masking
  • Hough line transform
  • Line averaging and extrapolation

Pipeline 

Frame → Grayscale → Blur → Canny → ROI Mask → Hough Lines → Average → Draw
   ↓        ↓        ↓       ↓         ↓           ↓          ↓       ↓
[Road]  [Gray]    [Smooth] [Edges]  [Trapezoid] [Lines]   [L/R]   [Overlay]

Key OpenCV Functions 

# 1. Preprocess
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray, (5, 5), 0)

# 2. Edge detection
edges = cv2.Canny(blur, 50, 150)

# 3. Region of interest (trapezoid on road)
mask = np.zeros_like(edges)
polygon = np.array([[
    (width * 0.1, height),
    (width * 0.45, height * 0.6),
    (width * 0.55, height * 0.6),
    (width * 0.9, height)
]], dtype=np.int32)
cv2.fillPoly(mask, polygon, 255)
masked = cv2.bitwise_and(edges, mask)

# 4. Hough lines
lines = cv2.HoughLinesP(
    masked,
    rho=2,
    theta=np.pi/180,
    threshold=50,
    minLineLength=40,
    maxLineGap=100
)

Line Averaging 

def average_slope_intercept(lines):
    left_fit = []
    right_fit = []

    for line in lines:
        x1, y1, x2, y2 = line[0]
        slope = (y2 - y1) / (x2 - x1)
        intercept = y1 - slope * x1

        if slope < 0:  # Left lane (negative slope)
            left_fit.append((slope, intercept))
        else:          # Right lane (positive slope)
            right_fit.append((slope, intercept))

    # Average the lines
    left_avg = np.average(left_fit, axis=0)
    right_avg = np.average(right_fit, axis=0)

    return left_avg, right_avg

Hough Transform Parameters

Parameter Purpose Typical Value
rho Distance resolution 1-2 pixels
theta Angle resolution π/180 radians
threshold Minimum votes 50-100
minLineLength Shortest line 40-100 pixels
maxLineGap Gap tolerance 50-100 pixels

Controls

Key Action
+/- Adjust Canny thresholds
s Save screenshot
q Quit

Running the Application 

python curriculum/applications/08_lane_detection.py

Official Documentation